Within the context of surface coatings, such as UV-crosslinkable coatings, polyester coatings, polyurethane coatings and acrylic coatings, among others, it is important to have an abrasion-resistant and scratch-resistant material and more generally to improve the mechanical resistance properties of the coating. This resistance is provided by the addition in these media (UV-crosslinkable, polyester, polyurethane or acrylic medium) of elements known for their mechanical resistance properties, such as polyamide or copolyamide powders.
The same problem arises in hydrophilic media, namely that of the compatibility of the hydrophobic PA or coPA powders that are added to these media.
Methods for functionalizing polyamide powders, in order to improve their compatibility with coatings, do exist. In most cases, this consists in introducing a functional compound into the polymer during its polymerization. However, the copolymerization of these functional compounds is often difficult to control, resulting in non-uniform distributions. Furthermore, the many process steps (grinding, drying, screening, etc.) often have to be adapted so as to preserve the reactivity of these functional compounds until the final powder is obtained.
It is therefore important to have polymer, particularly PA or coPA, powder particles that are compatible in various media, it being possible for this compatibility to be rapidly provided, in few steps and according to the customer's requirements, on a base product sold on a large scale, namely the polymer. This method of compatibilization must be applicable for all polyamide or copolyamide powders, independently of their production process.
The technical problem to be solved is a problem of compatibility between these media and said polymer powders, particularly PA or coPA powders, and of preservation of the active principles in the one medium without them being able to migrate out of said medium.
The Applicant has therefore discovered the possibility of adding powder particles to media, particularly polyamide or copolyamide particles, that are rendered compatible with such media by a grafting process carried out downstream of the production of said powders. This compatibility is made possible thanks to a process for grafting at least bifunctionalized grafts onto the powder particles, which make the powder particles reactive or compatible with respect to the media in which they may subsequently be added.
For example, in the case of a hydrophilic medium, the grafting onto a hydrophobic polyamide or copolyamide particle of a graft having a hydrophilic functional group makes it easier to disperse the particle in said medium, giving this particle hydrophilic properties.
The functionalization of the powder by grafting may be used to directly modify the surface properties of polymer, particularly polyamide or copolyamide, powders.